The objective of this program is to establish chronic respiratory disease (CRD) in mice using a strain of Mycoplasma pulmonis and to determine the effects of exposure to ozone (O3) and nitrogen dioxide (NO2) on the disease. The organism is administered to pathogen-free albino mice (CD1) via the intranasal route. Groups of 50 to 60 mice are exposed to O3, NO2, or combinations of these, 3 hrs/day for 1 to 20 days either before or after infectious challenge. Controls are exposed to filtered air. At weekly or biweekly intervals for 8 weeks after challenge, the lungs of four mice per exposure group are removed, homogenized, and plated out onto solid medium to determine colony-forming units of mycoplasmas. Four lungs are also fixed in formaldehyde and processed by conventional technique to be examined for histopathologic changes. Four mice per group are bled and the serum used in metabolic inhibition tests and also to detect concentrations of immunoglobulins by radial immunodiffusion. Comparison between pollutant-exposed and control mice are made using Student's t-test. Results to date show that multiple exposures to low pollutant concentrations produces the most significant enhancement of the disease.